1. Field of the Invention
This invention relates to tape transport systems, and more particularly to magnetic tape transport systems having a new improved tape path so that the same precise control of the movement of the tape during bidirectional, continuous or intermittent, operation presently possible in some systems, may be maintained in a more compact tape transport system.
2. Description of the Prior Art
Currently available tape transport systems employ capstan drive mechanisms that frictionally engage the tape and various servo means to achieve the desired control of tape movements. The magnetic tape must be moved at high nominal speeds, such as 75-150 inches per second (ips), but must at the same time be handled gently to avoid tape breakage, stretching or wear of the oxide surface. In addition, the tape must be maintained stably in a precise tape path as it passes the magnetic recording and reproducing head assembly. Complex problems arise in fulfilling each of these requirements for magnetic tape transport systems, which are also required to operate intermittently and bidirectionally. Magnetic tape transport systems must start and stop the tape in very brief time intervals and over very short distances (0.065 inches) in order to meet the demands of associated data processing equipment.
Vacuum chambers are employed as buffer mechanisms in these systems to provide tape loops of variable length interspersed in the tape path between high inertia storage reels and a low inertia capstan drive mechanism. The magnetic tape can be rapidly started and stopped between these buffer mechanisms while the relatively slow action of the high inertia storage reels is compensated by changes in the loop lengths within the adjacent buffer mechanisms. Accordingly, only the relatively short length, very low weight tape section located between the buffer mechanisms is acted on by the drive mechanism, so that start-stop times of the order of a relatively few milliseconds may easily be achieved.
U.S. Pat. No. 3,217,995, entitled Tape Buffer Means, issued to Jack F. Sweeney on Nov. 16, 1965, teaches a tape buffer providing transistory storage and a buffer means for a tape transpot to dampen the longitudinal oscillations caused by subjecting the tape to sudden start operations. The vacuum chambers are disposed in a V-shaped manner. U.S. Pat. No. 3,563,492, entitled Capstan Acceleration Control System for Wideband Instrumentation Magnetic Tape Transport, issued to Herman A. Ferrier, Jr. on Feb. 16, 1971 also teaches a pair of vacuum chambers arranged in a V-shaped manner. In both of these systems the tape reels are disposed about the base of the V formed by the two vacuum chambers.
U.S. Pat. No. 3,112,473, entitled Tape Storage Apparatus for Tape Processing Units, issued to Harold Wicklund and Hugo A. Panissidi on Nov. 26, 1963, teaches a pair of open ended, elongated upstanding adjacent inner and outer vacuum columns disposed on each side of the tape drive capstan. The unreeled tape forms loop within the vacuum chambers. This system according to U.S. Pat. No. 3,645,472, entitled High-Performance Tape Memory System, issued to Azmi S. Audeh on Feb. 29, 1972 may be used only in a stand alone unit and will not fit onto a standardized mounting rack of 19 by 24 inches as adopted by the data processing industry. U.S. Pat. No. 3,645,472 teaches a magnetic tape transport which provides a straight line tape threading path with substantial wrap about a drive capstan and adequately long buffer loops by adjacent disposition of similarly inclined but asymmetrically disposed vacuum chambers.
U.S. Pat. No. 3,823,895, entitled Automatic Tape Loading Apparatus and Method Therefor, issued to Hale M. Jones and James P. Urynowicz on July 16, 1974, teaches an automatic tape loading system for a magnetic tape transport system. The patent also teaches the use of auxiliary vacuum chambers in conjunction with vertically disposed vacuum chambers.
U.S. Pat. No. 3,380,682, entitled Magnetic Tape Transport, issued to Peter D. Georgantas, Ronald E. Loosen and Edward S. Kinney on Apr. 30, 1968, teaches a magnetic tape transport in which the tape passes between two planes. The vacuum chambers are arranged in a V and placed in one plane and the tape reels are placed in another plane. The purpose of this arrangement is to achieve a compact unit, but this unit is still larger than a standardized mounting rack.
In 1966 IBM developed a magnetic tape transport system which is typical of most tape transport systems in current use. The tape transport systems is described in U.S. Pat. No. 3,261,563, entitled Magnetic Tape Reel Control Servo System, issued on July 19, 1966 to Jesse I. Aweida, Donald K. Close and Henry C. Pao. The tape transport system includes a file reel, a first servo motor for driving the file reel, a machine reel, a second servo motor for driving the machine reel, a magnetic head mounted between the reels, a capstan for driving the tape bidirectionally past the magnetic head, a pair of parallel slack tape vacuum columns, each of which has an open end disposed adjacent each of the reels on opposite sides of the magnetic head, and a control system. The vacuum columns serve to greatly reduce the length of magnetic tape to be accelerated by the capstan thereby providing a smooth and rapid start-stop motion.
Presently IBM manufactures two standard magnetic tapes for use in the computer industry having bit densities of 1600 and 800 bits per inch and gaps of 0.6 inches between each block of data. IBM has recently developed a high density magnetic tape having a bit density of 6250 bits per inch with a gap of 0.3 inch between each block of data. The high density magnetic tape must be accelerated to 200 inches per second (ips) within 0.065 inch of magnetic tape in order to be fully utilized. The IBM tape transport system, described in U.S. Pat. No. 3,261,563, reaches a speed of 200 inches per second (ips) and reaches full speed within 0.065 inch of magnetic tape. The main problem with this system is that its dimensions are 30 inches wide, 66 inches high, and 30 inches deep. The size of a standard tape transport system in the computer industry is 19 inches wide, 24.5 inches high, and 26 inches deep, which allows mounting in a standard RETMA cabinet. Even when the speed and acceleration requirements of a computer system are reduced from 200 inches per second to 125 inches per second, the IBM tape transport system still cannot be reduced to the size of this tape transport system cabinet. This makes interfacing the tape transport system with a computer system difficult and expensive.
Another tape transport system has been developed by Wangco wherein a tape transport system described in U.S. Pat. No. 3,866,855, entitled Tape Tension and Velocity Conrol System, issued on Feb. 18, 1975 to Phillip Stuart Bryer, has a maximum magnetic tape speed of 75 inches per second, but its dimensions are such that it can be placed in a standard cabinet. The Bryer tape transport system comprises a frame on which are mounted a supply reel and a take-up reel, suitable drive motors and controls for the reels are mounted out of sight behind the reels, a length of magnetic tape extends between the reels and through a normal operative path comprising a first tape loop in a first vacuum buffer chamber, a pucker pocket or auxiliary buffer chamber, a magnetic head region, a drive capstan, and a second tape loop within a second vacuum buffer chamber. Assorted tape guides and rollers such as are situated along the tape path to help guide the magnetic tape. The two vacuum buffer chambers are open-ended and each vacuum buffer chamber includes a pair of parallel sidewall plates, one of which is common to both vacuum buffer chambers, a front plate, a back plate, and a base plate. The two base plates are disposed at opposite ends of the common sidewall plates. The supply reel and the take-up reel are disposed adjacent to each other and each reel is adjacent the first vacuum column.
The problem that arises is that when all the requirements of the new magnetic tape, including a tape speed of 125 inches per second and an acceleration to full speed within 0.065 inch, are met this tape transport system would not fit into a standard cabinet.